The consequences of increasing metal concentrations in surface and subsurface aqueous environments as a result of mining are not easy to anticipate due to the broad range of biogeochemical conditions and biological pathways in organisms (Allan, “Introduction: Mining and Metals in the Environment,” J. Geochem. Explor. 58:95 (1997)). To address this environmental problem, silica polyamine composites (SPCs) have been developed as one among many remediation technologies including organic polymer chelator resins and surface silanized silica gels (Zagorodni, “Ion Exchange Materials: Properties and Applications,” Elsevier Ltd. (2007); Beauvais et al., “Polymer-Supported Reagents for the Selective Complexation of Metal Ions: an Overview,” Reactive & Functional Polymers 36:113 (1998); Shiraishi et al., “Separation of Transition Metals Using Inorganic Adsorbents Modified with Chelating Ligands,” Ind. Eng. Chem. Res. 41(20):5065 (2002)). The SPCs combine the better capture kinetics and matrix rigidity of the surface modified silica gels with higher loading capacities of the polymer based chelator resins. SPCs are composed of a silica gel support covalently bonded to linear or branched water soluble chelating polyamines (Hughes et al., “Silica Polyamine Composites: New Supramolecular Materials for Cation and Anion Recovery and Remediation,” Macromol. Symp. 235:161 (2006); Beatty et al., “A Comparative Study of the Removal of Heavy Metal Ions from Water Using a Silica-Polyamine Composite and a Polystyrene Chelator Resin,” Ind. Eng. Chem. Res. 38:4402 (1999); Hughes et al., “Structural Investigations of Silica Polyamine Composites: Surface Coverage, Metal Ion Coordination, and Ligand Modification,” Ind. Eng. Chem. Res. 45:6538 (2006); Hughes et al., “Polymer Structure and Metal Ion Selectivity in Silica Polyamine Composites Modified with Sodium Chloroacetate and Nitriloacetic Acid (NTA) Anhydride,” Ind. Eng. Chem. Res. 47:6765 (2008); Rosenberg et al., “Removal of Low Level Mercury from Aqueous Streams Using Silica Polyamine Composites,” EPD Congress 2003 as held at the 2003 TMS Annual Meeting (San Diego, Calif.; 2-6 Mar. 2003). p. 285; Kailasam et al., “Characterization of Surface-Bound Zr(IV) and Its Application to Removal of As(V) and As(III) from Aqueous Systems Using Phosphonic Acid Modified Nanoporous Silica Polyamine Composites,” Ind. Eng. Chem. Res. 48:3991 (2009); Nielsen et al., “High-flow Metal Recovery from Acid Mine Drainage Utilizing Modified Silica Polyamine Composite Technology,” Chimica Oggi 26:42 (2008); and Allen et al., “Surface Oxidation of CO2+ and its Dependence on Ligand Coordination Number in Silica Polyamine Composites,” Inorg. Chim. Acta 363:617 (2010). The SPCs are synthesized via the following steps: acid washing of the silica gel surface, humidification, silanization with a mixture of methyltrichlorosilane (MTCS) and chloropropyltrichlorosilane (CPTCS), and finally addition of a polyamine and a modifying ligand (FIG. 1; Hughes et al., Macromol. Symp. 235:161 (2006)). SPCs show no shrinking or swelling, they withstand operating temperatures of up to 110° C., have anticipated stability to radiolytic decomposition, and they exhibit long usable lifetimes due to their rigid macrostructure and the multipoint anchoring of the polymer (Beatty et al., Ind. Eng. Chem. Res. 38:4402 (1999)). Prior studies on SPCs revealed that usage of MTCS and CPTCS in a 7.5:1 ratio on modified silica gel gave improvements in metal ion capacities and mass transfer kinetics under low-pH aqueous extraction conditions (Hughes et al., Ind. Eng. Chem. Res. 45:6538 (2006)). The improved metal selectivity capacity for a particular metal atom is thought to be caused by the greater availability of coordinating sites.
The oxine ligand (i.e., 8-hydroxyquinoline) has long been known to be a versatile functional group for complexing transition metal ions and in particular trivalent ions. The solvent extraction lixavent, Kelex 100, is an alkyl-modified oxine that has found extensive use in solvent extraction, particularly for the recovery of gallium from Bayer solutions produced in the aluminum refining industry (Matsuda et al., Nippon Kagaku Kaishi 415 (1990)). Several groups have reported the impregnation of Kelex 100 into polystyrene resins (Nakayama et al., “Recovery of Gallium(III) from Strongly Alkaline Media Using a Kelex-100-Loaded Ion-Exchange Resing,” Ind. Eng. Chem. Res. 36:4365 (1997)). Covalent binding of the oxine ligand to water soluble polymers (Rongnong et al., Naturforsch 47b:1300 (1992)), as well as polystyrene resins via azo linkages (Davies et al., “Syntheses of Metal Complexing Polymers. IV. Polymers Containing Miscellaneous Functional Groups,” Appl. Chem. 9:368 (1959)), Friedel-Krafts chemistry (Sugii et al., “Preparation and Properties of Chelating Resins Containing 8-Hydroxyquinoline,” Chem. Pharm. Bull. 26(3):798 (1978)) or copolymerization with resorcinol (Vernone et al., “Chelating Ion-Exchangers Containing 8-Hydroxyquinoline as the Functional Group,” Anal. Chim. Acta 63:403 (1973)) has been reported. Covalent bonding to aminopropyl functionalized silica gels via the diazotization method (Fulcher et al., “Synthetic Aspects of the Characterization of Some Silica-Bound Complexing Agents,” Anal. Chim. Acta 129:29 (1981)) and the Mannich reaction (Pyell et al., “Preparation and Properties of an 8-Hydroxyquinoline Silica Gel, Synthesized via Mannich Reaction,” Anal. Chem. 342:281 (1992)) also been reported. Although some of these materials showed promise for sequestering metal ions in general they had significant problems with mass transfer kinetics (organic polymers) or low capacities (silica gels). Furthermore, the selectivity of these oxine modified solid phase adsorbents for various metals was not well defined in the prior work.
All patents, patent applications, provisional patent applications and publications referred to or cited herein, are incorporated by reference in their entirety to the extent they are not inconsistent with the teachings of the specification.